Alzheimer's disease (AD), the most common dementing disorder of late life, is a major cause of disability and death in the elderly. AD is characterized and diagnosed by distinctive neuropathological alterations including extracellular deposits of the -amyloid (A) peptide. Epidemiological investigations have demonstrated that AD is a complex, age-related disorder with numerous proposed genetic and environmental etiologies. Human genetic studies have shown that altered dosage and mutations in the amyloid precursor protein gene as well as mutations in presenilin 1 and presenilin 2 genes all cause early-onset AD, while the APOE gene is major risk factor in late-onset AD. Considerable evidence suggests that these genetic factors alter A metabolism and/or A deposition. However, the AD genes identified thus far account for less than 30% of genetic risk for AD. Due to the inherent variability and genetic heterogeneity in late-onset neurodegenerative disorders, the identification of the remainder of the genetic and environmental factors that modulate AD risk have proven extremely difficult. Over the past decade and a half, several groups, including our own, have focused on the development of accurate and defined mouse models of AD, in which both the genetic background and environmental exposure can be precisely and reproducibly modified in an effort to gain insight into factors that modify APP processing, the production and deposition of A peptides, the onset of dementia and the neuropathological abnormalities that occur in AD. In the previous funding period of this grant application, we generated congenic strains, in which a human AD transgene was transferred into different inbred mouse strains. We subsequently characterized the effects of different inbred genetic backgrounds and specific genetic alterations on A metabolism and deposition and other AD phenotypes and identified unique mouse genetic loci that regulate metabolism and deposition. In addition, in preliminary studies we determined that the effects of an environmental factor, namely high-fat/high-cholesterol diets, on brain A levels are dependent upon the genetic background of the mice. The current studies seek to expand and extend these studies with a focus on genetic and environmental factors that regulate A metabolism and deposition in two inbred mouse strains with the most divergent A phenotypes, C57BL/6J and A/J, using the unique genetic resources available for these strains. The specific aims of the current proposal are to: 1) Identify mouse chromosomes with gene(s) that regulate A metabolism and deposition. 2) Identify and characterize genetic loci that regulate A deposition. 3) Characterize genetic loci responsible for diet-induced alterations in A metabolism and deposition.